Reference voltage-switching unit

ABSTRACT

A reference voltage-switching unit comprising a dual DC voltage power supply which provides +V DC and -V DC voltages across three of its output terminals, one of which is assumed to be at ground. The three terminals are connected to two unit output terminals through a switching unit which includes a voltage divider and three sets of SPDT contacts. The positions of the three sets of contacts are controlled as a function of the binary states of three stages of a three-stage ring counter. As the counter advanced through its eight-state cycle, the positions of the three sets of contacts vary so that the voltage across the unit output terminals follows a cyclically recirculating pattern including the values of +V, +V/2, O, -V/2,-V, -V/2 O and +V/2.

United States Patent [72] lnventors Thomas 0. Paine Administrator of theNational Aeronautics and Space Administration with respect to aninvention of; Edgar S. Davis, Pasadena, Calif. [21] Appl. No. 21,906[22] Filed Mar. 23, 1970 [45] Patented Sept. 28, 1971 [54] REFERENCEVOLTAGE-SWITCHING UNIT 9 Claims, 2 Drawing Figs.

[52] 11.8. C1 307/81, 307/223, 307/227, 328/186 [51] Int. Cl. [103k23/03 [50} Field of Search 307/81, 223,227; 328/104, 186

[56] References Cited UNITED STATES PATENTS 2,899,567 8/1959 Romano307/81 3,100,851 8/1963 Ross et al 328/186X 3,215,860 11/1965 Neumann.328/186X 3,235,840 2/1966 Sturm 307/223 X Primary Examiner- Robert K,Schaefer Assistant Examiner-William .1. Smith Attorneys-4. H. Warden,Paul F. McCaul and G. T. McCoy ABSTRACT: A reference voltage-switchingunit comprising a dual DC voltage power supply which provides +V DC andV DC voltages across three of its output terminals, one of which isassumed to be at ground. The three terminals are connected to two unitoutput terminals through a switching unit which includes a voltagedivider and three sets of SPDT contacts. The positions of the three setsof contacts are controlled as a function of the binary states of threestages of a three-stage ring counter. As the counter advanced throughits eight-state cycle, the positions of the three sets of contacts varyso that the voltage across the unit output terminals follows acyclically recirculating pattern including the values of +V, +V/2, O,*V/2,V, -V/2 O and +V/2.

BINARY RING COUNTER 25 ,1, I I M- I O9 DI0 K2 I n |z K3 I RESET 3 42asssr g 43 I SET 1 I SET 1 I I s 1- s I c c: I c; c; I I m1 K29 I mus, Issr I 1 SET I I 521' I l I I INPUT PULSE I 2 I I 0 I 0 o I so I i T T ITI s| I s2 sa m h nes'ef I I I8 K 1 RESET RESET I K u 10 I5 I an :1 KSAII RI I I neon I II IFIER I6 1 our 1 R2 I m1: -v I I PATENTEDSEP28I97I I3,609,387

sum 2 0F 2 FIG.2

COUNTER STATE OUT OUTPUT VOLTAGE A B c o E F e H A V T as,

EDGAR S. DAVIS INVIENTOR.

ATTORNEYS REFERENCE VOLTAGE-SWITCHING UNIT ORIGIN OF INVENTION Theinvention described herein was made in the performance of work under aNASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act of 1958, Public Law 85-568 (72 State.435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention generally relates to voltage control circuitry and, moreparticularly, to a relay-controlled voltage switching unit whose outputvoltage follows a cyclically recurring pattern.

2. Description of the Prior Art In some instrumentation applications aneed exists for a reference voltage which follows a cyclically recurringpattern and which can be easily controlled by a simple single properlytimed command. Such a need arose in the design of scanning circuitry fora tracker of the star Canopus which was selected to control theroll-angle of a spacecraft. During the course of a full sun orbit by thespacecraft, the star field, in which Canopus is one of many brightobjects, appears to rotate once about the ecliptic pole, with the resultthat the sun-spacecraft- Canopus (cone) angle varies cyclically between75 and 105.

The Canopus star tracker provides spacecraft roll-error anglemeasurement by incorporating a scanning arrangement which repetitivelyscans a slit across a small region of the image field of view of thetracker. The tracker measures a phase angle which provides an errorsignal which is proportional to the subtended angle between the line ofsight to the star and a reference axis in the mounting plane of the startracker.

Due to the presence of background light and an excessive number ofbright stars, near the same cone angle as Canopus, it is necessary thatthe trackers field of view be restricted in cone angle to a fraction,such as ll, of the total variation of the sun-spacecraft-Canopus (cone)angle which varies over a range of 30. This requires that the narrowfield of view be deflected in cone angle in five discretely steppedoverlapping offsets to follow the variations in the Canopus cone angle.Since star trackers are likely to be used on most interplanetary spacemissions with each mission beginning and ending at a different point inthe star cone angle cycle, it is important that the deflection voltageprogram be cyclical, and be startable at any point in the cycle. It isalso important that the deflection voltage programmer have anondestructive memory ofits state since a star tracker may be turned offand then back on during a particular mission.

Since the tracker is to be used in a spacecraft, it is important thatthe circuitry which generates the reference voltage be highly reliableyet simple, so as to minimize malfunctioning and practically eliminateall maintenance requirements. Also, it is important that the circuitrybe responsive to simple command signals either from a ground station orfrom onboard equipment.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of thepresent invention to provide a new voltage-switching unit, whose voltageoutput follows a cyclically recurring pattern.

Another object of the present invention is to provide a reliable yetsimple voltage-switching unit which provides an output voltage whichvaries in magnitude and polarity in discrete steps in a cyclicallyrecurring pattern.

A further object of the present invention is to provide a reliable,relatively simple voltage-switching unit which is controllable by asequence of command signals in order to provide a cyclically recurringpattern of an output voltage with each step in the pattern being ofaselected voltage and polarity.

These and other objects of the invention are achieved by providing avoltage-switching unit which includes a dual DC voltage power supply,connected to a pair of output terminals,

through a voltage-switching section and a voltage divider. The

voltage-switching section includes several single-pole doublethrow(SPDT) contacts which are controlled as a function of the states of amultistage binary counter, such as a relay-type multistage ring counter.The connections between the output terminals and the power supply, whichcontrol the output voltage, depend on the positions of the SPDT contactswhich are in turn controlled by the stages of the counter. As thecounter advances through its binary states the SPDT contacts positionsvary so that the output voltage follows a cyclically recurring pattern.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic and blockdiagram of the present invention; and

FIG. 2 is a chartlike diagram useful in explaining the operation of thecircuitry, shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now directed toFIG. 1 wherein the present invention is shown to include a dual DCvoltage power supply 10, comprising a transformer 11, whose inputterminals across the primary winding are assumed to be connected to anAC powerline. The transformer secondary winding is shown connected to arectifier and filter 12 which has three output lines, designated 15, 16and 17. Line 15 is assumed to be at +V DC volts above line 16 which maybe assumed to be at ground, while line 17 is at V volts with respect toground.

The three output lines of the power supply 10 are connected to twooutput terminals 18 and 19 of the present invention, through avoltage-switching section 20. It is terminals 18 and 19 across which theoutput voltage V of the present invention is applied as a cyclicallyrecurring pattern.

The voltage-switching section 20 comprises a voltage divider whichconsists of two equal resistors RI and R2 and three sets of single-poledouble-throw (SPDT) contacts, designated KlA, K2A and K3A. The twopositions of each set of contacts are designated as the SET and RESETpositions. The three sets are diagrammed in their SET positions. Thethree sets of contacts are separately controlled by three stages S1, S2and S3, which form a three-stage binary ring counter 25.

Each counter stage is either in a set S state or in a reset R state. Inthe present invention the positions of the three sets of contacts KlA,K2A and K3A correspond to the states of the three stages S1, S2 and S3.As diagrammed, the three stages are assumed to be in their S states,since the three sets of contacts are shown in their SET position.

As is appreciated by those familiar with the art, the combined states ofthe three stages of counter 25 define eight (2) possible counter stateswhich represent one complete counter cycle. Thus during a completecounter cycle, the three sets of contacts assume eight differentcombinations of positions as diagrammed in the bottom half of FIG. 2.

For example, when the counter is in state A, the three stages 81, S2 andS3 are in their S states and consequently the sets of contacts are intheir SET positions (as shown). As a result, line 16 of the power supply10 which is at 0 volts is connected to output terminal 18 through theSET position of contact C3, while line 17 at V volts is connected toterminal 19 through the SET positions of contacts KlA and K2A. Thus, thepotential difference between terminals 18 and 19 is +V as indicated bybar 31 in FIG. 2.

During the next stage B of the counter, the three stages are in their Rstates. As a result, all the three sets of contacts KIA,

K2A and K3A are in their RESET positions. Consequently, line 16 which isat ground is connected to terminal 19 through the RESET position of K2A.+V volts is applied across the two resistors R1 and R2 since line isconnected to R1 through the RESET position of KlA. Since the junctionpoint of the two equal resistors is connected to tenninal 18 through theRESET position of K3A, +V/2 is applied across terminals 18 and 19. The+V/2 potential difference is designated in FIG. 2 by bar 32.

During the next state C of the counter 25, when stages 51 and 52 remainin the R state and only the least significant stage in the binary order,i.e., S3 is switched to the S state, contact sets KIA and K2A are intheir RESET positions and only K3A is in the SET position. Consequently,0 volts is applied across terminals 18 and 19. This is the case since inthis counter state, line 16 is connected to terminal 18 through the SETpositions of contacts K3A while at the same time it, line 16, isconnected to terminal I9 through the RESET position of K2A. This 0output voltage is represented in FIG. 2 by bar 33.

The other discrete steps of the output voltage of V/2, V, V/2, 0 and+V/2, which are designated by bars 34-38, respectively, are producedduring the succeeding counter states, designated D through H; Thus, forthe counters eight states in each cycle, eight discrete output voltagesteps are produced. These steps follow this cyclically recurring patternas the counter recycles during a subsequent cycle.

From the foregoing it is thus seen that the cyclically recurring statepattern of a multistage binary counter are used to control the formationof discrete steps of an output voltage which also follows a cyclicallyrecurring pattern. In the particular embodiment, a three-stage counter,having an eightstate cycle, is used to control the formation of eightdiscrete steps of the output voltage V These steps are formed by usingthe three counter stages to control these SPDT sets of contacts of unit20 and thereby control the connections between a dual DC voltage powersupply and a pair of output terminals.

In the particular embodiment, which is diagrammed in FIG. 1, each stageof the counter is shown comprising, in addition to a pair of capacitorsand four diodes, a double-coil, latching relay and a SPDT set ofcontacts. The switching section 20 and the counter can be easily andconveniently implemented as one unit by employing three double-coillatching relays of the double-pole double-throw (DPDT) configuration. Insuch an arrangement one set of contacts of each relay is used as part ofa counter stage and the other set is used as part of the switchingsection 20 which the relay has to control.

Such an arrangement is assumed in FIG. 1, in which the three relays aredesignated K1, K2 and K3. Relay K1 has double coils, designated bynumeral 41, which control the positions of contacts KlB which form partof stage S1 and con tacts KIA. Similarly, K2 comprises coils 42 withcontact sets K28 and KZA, while K3 comprises coils 43 with contact setsK38 and K3A. Such an implementation minimizes the number of elementsneeded to form the switching section 20, as well as the problems ofcontrolling contact sets KIA, K2A and K3A in order to produce thediscrete steps of the output voltage. Such double-coil latching relayswith a DPDT configuration are available commercially, such as forexample a Teledyne relay type 0420-l 2.

The operation of the ring counter 25 may be described as follows. Thestate of the binary ring counter is changed by a momentary closure of atransistor switch Q1. The transistor may be driven by an input pulse 50,which may be furnished either by a telemetered command or from anonboard source. FIG. I shows the three relays with both sets of contactsof each relay in the SET positions. Each of the two relay coils operateson a capacitor discharge, and the necessary capacitor charge is providedby a source of negative voltage, such as -30v., connected to the movingcontact of C30 through a resistor R3.

Initially, capacitors C1, C3 and C5 are charged to 30 volts throughdiodes D7, D9 and DH and the counter SET contacts of the three relays.Diodes D2, D4 and D6 prevent charging of capacitors C2, C4 and C6. Amomentary closure of transistor Q1 is effected by the input pulse. Thisprovides a low resistance path which discharges capacitor C1 through thereset coil of relay Kl to ground, capacitor C3 through the reset coil ofrelay K2 to ground, and capacitor C5 through the reset coil of relay K3,transferring both sets of contacts of each relay from the SET to theRESET position and shifting the scan reference one step from state A tostate B as shown in FIG. 2. Only capacitor C6 can now charge to 30 voltsthrough diode D12 since, diodes D1, D2, D3, D4 and D5 prevent chargingof the other capacitors.

On the next impulse to switch 01, capacitor C6 discharges through theSET coil of relay K3, changing both sets of its contacts from the RESETto the SET position, shifting the scan reference one step from state Bto state C as shown in FIG. 2. Since the coils of relays K1 and K2 werenot impulsed, their contacts remain in RESET position. Subsequentimpulse operation of switch 01, produces the series of relay contactstates shown in the table in FIG. 2, and this sequences the outputvoltage from state C to states D, E, F, G and H, and eventually to stateA, at which the sequence repeats.

It is apparent that by such a switching sequence, it is possible toplace the output voltage at any step, as for example at state D, of thecounter when the voltage is V/2 and then proceed by sequential impulsingthe counter to pass through a series of steps represented by states E,F, G, H, A, B, C, etc.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art and consequently it isintended that the claims be interpreted to cover such modifications andequivalents.

What is claimed is:

.1. A voltage switching unit, comprising:

a dual direct-current voltage power supply;

first and second output terminals;

interconnecting means including it switchable means for connecting theoutput of said power supply to said output terminals each switchablemeans being switchable between an active state and an inactive state;and

binary counting means of n stages for controlling the states of said nswitchable means to control the voltage across said output terminals tofollow a cyclically recurring pattern of 2" levels as a function of thechanges of the binary states of the h stages of said binary countingmeans, each of said It stages controlling the state of a differentswitchable means, with at least two of said stages being in a binarystate, whereby at least two of said It switchable means are in theiractive state, to provide selected ones of said 2" levels.

2. The arrangement as recited in claim I wherein said power supply hasfirst, second and third output lines, said first line being at +V voltsabove said second line and said third line being at -V volts below saidsecond line and said cyclically recurring pattern of said output voltageincludes three levels at which the voltage difference between said firstand second output terminals is +V volts, 0 volt and V volts and eachswitchable means is a single-pole double-throw switch which is either inits active state or inactive state when the stage of the binary countingmeans with which it is associated, is in either a first binary state ora second binary state respectively, each switch providing a first signalpath therethrough when being in said active state and a second signalpath when being in said inactive state.

3. The arrangement as recited in claim 2 wherein said voltage levelsinclude the levels of +V volts, 0 volt and V volts.

4. The arrangement as recited in claim 3 wherein n is sufiiciently largeand said voltage levels includes levels of +l/xV and -l/.rV where x isan integer greater than 1.

5. The arrangement as recited in claim 4 wherein n=3.

6. The arrangement as recited in claim 5 wherein each set of contacts isa first set of contacts of a dual-coil relay with two sets ofsingle-pole doublethrow contacts, with the second set of said contactsand said dual coil forming part of the binary stage which is associatedwith said first set of contacts.

7. The arrangement as recited in claim 1 wherein said interconnectingmeans include voltage dividing means whereby said cyclically recurringpattern of said output voltage includes two levels at which the voltagedifference between said first and second output -tenninals is betweenand +V volts and between 0 and V volts.

8. The arrangement as recited in claim I wherein said switchable meanscomprises It sets ofsingle-pole double-throw contacts, said power supplyhas first, second and third output lines which are at +V volts, 0 voltand V volts respectively, said interconnecting means comprisesinterconnecting lines which interconnect said power supply output lineswith said output terminals through said n sets of contacts, and whereinsaid binary-counting means comprises an n stage binary counter, eachcounter stage being associated with a different one of said n sets ofcontacts, for controlling the position of the associated set of contactsas a function of the stages binary state, whereby the output voltageacross said output terminals follows a cyclically recurring pattern as afunction of the positions of said n sets of contacts.

9. The arrangement as recited in claim 8 wherein each set of contacts isa first set of contacts of a dual-coil relay with two sets ofsingle-pole double-throw contacts, with the second set of said contactsand said dual-coil forming part of the binary stage which is associatedwith said first set of contacts.

1. A voltage switching unit, comprising: a dual direct-current voltagepower supply; first and second output terminals; interconnecting meansincluding n switchable means for connecting the output of said powersupply to said output terminals each switchable means being switchablebetween an active state and an inactive state; and binary counting meansof n stages for controlling the states of said n switchable means tocontrol the voltage across said output terminals to follow a cyclicallyrecurring pattern of 2n levels as a function of the changes of thebinary states of the n stages of said binary counting means, each ofsaid n stages controlling the state of a different switchable means,with at least two of said stages being in a binary state, whereby atleast two of said n switchable means are in their active state, toprovide selected ones of said 2n levels.
 2. The arrangement as recitedin claim 1 wherein said power supply has first, second and third outputlines, said first line being at +V volts above said second line and saidthird line being at -V volts below said second line and said cyclicallyrecurring pattern of said output voltage includes three levels at whichthe voltage difference between said first and second output terminals is+V volts, 0 volt and -V volts and each switchable means is a single-poledouble-throw switch which is either in its active state or inactivestate when the stage of the binary counting means with which it isassociated, is in either a first binary state or a second binary staterespectively, each switch providing a first signal path therethroughwhen being in said active state and a second signal path when being insaid inactive state.
 3. The arrangement as recited in claim 2 whereinsaid voltage levels include the levels of +V volts, 0 volt and -V volts.4. The arrangement as recited in claim 3 wherein n is sufficiently largeand said voltage levels includes levels of +1/xV and -1/xV where x is aninteger greater than
 1. 5. The arrangement as recited in claim 4 whereinn
 3. 6. The arrangement as recited in claim 5 wherein each set ofcontacts is a first set of contacts of a dual-coil relay with two setsof single-pole double-throw contacts, with the second set of saidcontacts and said dual coil forming part of the binary stage which isassociated with said first set of contacts.
 7. The arrangement asrecited in claim 1 wherein said interconnecting means include voltagedividing means whereby said cyclically recurring pattern of said outputvoltage includes two levels at which the voltage difference between saidfirst and second output terminals is between 0 and +V volts and between0 and -V volts.
 8. The arrangement as recited in claim 1 wherein saidswitchable means comprises n sets of single-pole double-throw contacts,said power supply has first, second and third output lines which are at+V volts, 0 volt and -V volts respectively, said interconnecting meanscomprises interconnecting lines which interconnect said power supplyoutput lines with said output terminals through said n sets of contacts,and wherein said binary-counting means comprises an n stage binarycounter, each counter stage being associated with a different one ofsaid n sets of contacts, for controlling the position of the associatedset of contacts as a function of the stage''s binary state, whereby theoutput voltage across said output terminals follows a cyclicallyrecurring pattern as a function of the positions of said n sets ofcontacts.
 9. The arrangement as recited in claim 8 wherein each set ofcontacts is a first set of contacts of a dual-coil relay with two setsof single-pole double-throw contacts, with the second set of saidcontacts and said dual-coil forming part of the binary stage which isassociated with said first set of contacts.